Means for forming voids in precast concrete structural members



2,949,658 MEANS FOR FORMING vows IN PRECAST CONCRETE STRUCTURAL MEMBERS N. A. CONN Aug. 23, 1960 Filed Oct. 3, 1956 MEANS FOR FoRMiNo voros 1N PRECAST CONCRETE STRUCTURAL MEMBERS Nathan A. Conn, Washington, D.C., assignor to American-Marietta Company, Chicago, 111., a corporation of Illinois Filed Oct. 3, 1956, Ser. No. 613,726

' 6 Claims. c1. 25-128) This invention relates to means for forming voids in precast concrete structural members, and is particularly concerned with the formation of voids having a noncircular cross section and tapered ends to provide a structure having greater strength at its ends.

In accordance with the invention, a plurality of inflatable rubber tubes encased in a casing of canvas, or other similar inexpensive material, are positioned in a mold. After the rubber tubes are inflated, concrete is poured in the mold around the canvas casing while it is distended by the rubber tubes. After the concrete has set sufliciently, the rubber tubes are deflated and removed to leave a void in the molded concerte member. The canvas casing may be removed with the collapsed rubber tubes, if its outer surface is treated to prevent it from sticking to the concrete, or it may be left in the concrete member.

The inflatable rubber tubes operate as a unit and, in the preferred embodiment shown in the drawings and described herein, comprise one main tube and four auxiliary tubes. The main tube has a cylindrical center section extending over the major portion of its length and tapering end sections extending longitudinally from opposite ends of the center section. The auxiliary tubes are arranged longitudinally of the main tube and are spaced 90 apart around the periphery of the center section. The auxiliary tubes are preferably secured to the main tube in any suitable manner, as, for example, by adhesion or by vulcanization.

The auxiliary tubes form corner extensions around the cylindrical center section of the main tube to impart a substantially square cross section to the contiguous section of the canvas casing when the rubber tubes are inflated. The auxiliary tubes are of approximately the same length as the cylindrical center section of the main tube and, therefore, do not interfere with the shape of the tapering end sections.

The canvas casing is preferably shaped to conform to the shape of the inflated rubber tube unit, but may be wrapped around the rubber tube unit if desired. One

end of the canvas casing is releasably secured to a pressure head to which one end of each of the rubber tubes is secured. The canvas casing may be released from the pressure head or may be cut adjacent the end of the concrete if it is to remain in the concrete member.

After the rubber tubes, and the canvas casing, if it is to be removed, are removed from the concrete structural member, the void left in the concrete has a square cross section through most of its length. The ends of each void are conical, with the small ends of the conical portions of the void at opposite ends of the concrete structural member. It is desirable that the void have a square cross section rather than a circular one because such configuration saves more concrete and further reduces the weight of the concrete structural member without loss of strength. The reduced diameter of the void at both ends of the concrete structural member provides Patented Aug. 23, 1960 adidtional strength at each end of the member and also makes it easier to plug the ends.

The structure by means of which the above mentioned and other advantages of the invention are attained will be described in the following specification, taken in conjunction with the accompanying drawings, showing a preferred illustrative embodiment of the invention, in which:

Figure l is a perspective view of a concrete structural member embodying the invention;

Fig. 2 is a fragmentary longitudinal sectional view through a mold box with the void forming unit inflated in the concrete;

Fig. 3 is a cross sectional view, 33 of Fig. 2;

Fig. 4 is a cross sectional view, 4-4 of Fig. 2; and

Fig. 5 is a fragmentary longitudinal view showing the deflated rubber tubes being removed from the concrete structural member.

In the drawings, the reference numeral 2 indicates a molding box comprising a bottom 3 and upstanding side walls 4. An air pressure head 5 is movably supported in any suitable manner so that it may be moved vertically relative to the molding box. An inflatable rubber tube 6, shaped to provide a cylindrical center section 7 and tapering conical end portions 8 and 9 when it is inflated to a predetermined extent by air pressure head 5, has an open neck 10 attached to head 5. Four auxiliary rubber tubes 11 also have open necks 12 attached to head 5 so that all of the rubber tubes may be inflated simultaneously. The air pressure head is controlled so that uniform pressure is applied to each tube unit to insure uniform inflation of the tubes in every precast concrete structural member.

Tubes 6 and 11 are positioned within a canvas casing 13 which may be in the form of a bag or may comprise a flat sheet wrapped around the rubber tubes. The open end of casing 13 is folded between an apertured disc 14 and pressure head 5. Disc 14 and pressure head 5 are clamped together by any suitable means, such as bolts, to hold the open end of casing 13 between them. Disc 14 is provided with apertures through which the necks 10 and 12 of tubes 6 and 11 project.

When the molding box 2 is set up to form a concrete structural member the air pressure head 5 is positioned a short distance above the open top of the box with the rubber tubes and canvas casing suspended centrally of the box. Air pressure head 5 is supported in predetermined relationship to the open top in any suitable manner. A valve 15, connecting head 5 to an air pressure line 16, is then opened to inflate the rubber tubes to a predetermined extent.

The position of air pressure head 5 is such that the bottom of tube 6 and casing '13 are pressed against the bottom 3 of the molding box to form a closed circular area of predetermined size centrally of the box in a'plane contiguous to the bottom. The canvas casing is distended symmetrically by the inflated rubber tubes and projects above the upper edge of the box a distance suflicient to enclose a circular area in the plane of the upper end of the box substantially equal to the area of the closed circle at the bottom of the box.

The canvas casing 13 tapers outwardly from each of the closed circular areas at the opposite ends of the molding box as it extends towards the cylindrical center section of tube 6. The canvas casing extending around the cylindrical center section of the tube also encloses the four auxiliary tubes 11 which are inflated and are positioned longitudinally adjacent the center section of tube 6. Tubes 11 are spaced from each other and are aligned diagonally with the corners of side walls 4 of the taken along the line taken along the line molding box. The tubes 11 are preferably secured to the outer surface of the cylindrical center section of tube 6 in any suitable manner, as, for example, by vulcanization or adhesion. Instead of securing tubes 11 to the outer surface of tube 6, they may be secured to the inner surface of casing 13, if desired. Itisobvious that if the casing is formed into a bag having a restricted neck, the tubes 11 must be secured thereto before the bag is completely fabricated.

The diameter of tubes 11 relative to the diameter of tube '6 is so chosen and tubes 11 are so positioned, relative to either tube 6 or casing 13, that when the casing and tubes are assembled, and all of the tubes are inflated, a straight line extending from the outer surface of any tube 11 to the outer surface of any adjacent tube 11 will be tangential to the outer surface of tube 6 midway between the two tubes 11. Accordingly, the tubes 11 distend the adjacent portion of the canvas casing into rectangular cross section with the walls of the rectangle parallel to'the walls of the molding box.

The tubes 11, which are positioned adjacentthe cylindrical center section of tube 6 and extend longitudinally thereof, are slightly shorter than the center section of tube 6. The tapered ends of casing 13 extend uniformly past the juncture of the tapered end of tube 6 and the cylindrical center section thereof to terminate at the ends of the tubes 11 which define the area of square cross section. In other words, the taper of the casing 13 extends substantially uniformly from the end of the area of square cross section, defined by tubes 11, to the end of the casing.

When the casing 13, with inflated tubes 6 and 11 housed therein, is positioned in molding box 2 with pressure head holding the casing and tubes in predetermined relationship to the molding box, the concrete 17 is poured around the canvas casing and allowed to set. If the canvas is to be re-used it is treated to prevent it from sticking to the concrete. Otherwise it is left in the mold. After the concrete has set sufliciently, the valve 15 is opened to deflate the rubber tubes. Pressure head 5 is then lifted to remove the rubber tubes from the concrete, leaving a void of the desired shape. If the canvas is to be left in the concrete it may be released at its upper end by releasing the pressure holding head 5 and disc 14 together, or the neck of the casing may be cut close to the end of the concrete structural member.

The removal of the deflated rubber tubes leaves a concrete member 18 having a void having a square cross section over most of its length, and tapering at each end to provide conical ends terminating in a small circle 19 at each end of the concrete structural member.

While I have described a preferred embodiment of my invention in detail, it will be understood that the description thereof is illustrative, rather than restrictive, as many details may be modified or changed without departing from the spirit or scope of my invention. For example, the number and arrangement of the rubber tubes may be altered to provide voids having shapes other than of square cross section. Accordingly, I do not desire to be restricted to the exact construction described.

I claim:

1. Means for forming a void having an elongated rectangular center section and tapered ends in a precast concrete structural member of elongated rectangular shape, with the outer surface planes of said structural member substantially parallel to the surface planes of the center section of said void and the cross sectional area of said void decreasing gradually from each end of said center section to each end of said structural member, said means comprising an inflatable, main rubber tube having tapered ends, a plurality of elongated auxiliary inflatable rubber tubes of smaller cross sectional diameters, positioned longitudinally in transversely spaced relative to each other against said first mentioned tube between said tapered ends, and an outer non-elastic, flexible casing enclosing said main tube and said auxiliary tubes, the cross sectional diameters of the auxiliary tubes being of such size relatively to the main tube, and of such spacing thereabout, so that when the tubes are inflated the outer casing enclosing the tube assembly will be stretched taut thereabout, so as to form substantially planar sections between adjacent auxiliary tubes, each of said planar sections con tacting said main tube tangentially along a longitudinal line.

2. Means for forming a void in a precast concrete structural member comprising an inflatable main rubber tube having a cylindrical center section extending over the major portion of its length, and a tapered end section extending longitudinally from opposite ends of said cylindrical section, a plurality of elongated auxiliary inflatable rubber tubes arranged longitudinally in transversely spaced relation to one another and in contiguous relationship to the cylindrical center section of said main tube, said auxiliary tubes each having a length no greater than the length of the cylindrical portion of said main tube, and an outer non-elastic, flexible casing enclosing all of said tubes, said casing being distended by the spaced tube and said tapered section of the main tube when said tubes are inflated, the cross sectional diameters of the auxiliary tubes being of such size relatively to the main tube, and of such spacing thereabout, so that when the tubes are inflated the outer casing enclosing the tube assembly will be stretched taut thereabout, so as to form substantially planar sections between adjacent auxiliary tubes, each of said planar sections contacting said main tube tangentially along a longitudinal line.

3. Means for forming a void in a precast concrete structural member comprising an inflatable main rubber tube having a cylindrical center section extending over the major portion of its length, and a tapered end section extending longitudinally from opposite ends of said cylindrical section, a plurality of elongated auxiliary inflatable rubber tubes of smaller cross sectional diameter than said main tube arranged longitudinally in contiguous relationship to the cylindrical center section of said main tube, said auxiliary tubes being spaced on axes of the main tube, which axes are from one another when all of said tubes are inflated, said auxiliary tubes each having a neck connected to an air pressure head adapted to inflate said main tube, and a non-elastic, flexible casing enclosing all of said tubes, said casing being of a size and shape as to be stretched to a substantially square cross sectional form about said tube assembly between said tapered ends and to conform to the general contour of said tapered ends when the tube assembly is inflated.

4. Means for forming a void in a precast concrete structural member comprising an inflatable main rubber tube having a cylindrical center section extending over the major portion of its length, and a tapered end section extending longitudinally from opposite ends of said cylindrical section, a plurality of elongated auxiliary inflatable rubber tubes arranged longitudinally in contiguous relationship to the cylindrical center section of said main tube, said auxiliary tubes being spaced on axes of the main tube, which axes are 90 from one another when all of said tubes are inflated, an air pressure head connected to each of said tubes, a disc adjacent said air pressure head, and a non-elastic, flexible casing enclosing all of said tubes, said casing having an open end clamped between said disc and said air pressure head to hold it in predetermined relationship to said tubes, the cross sectional diameters of the auxiliary tubes being of such size relatively to the main tube, and of such spacing thereabout, so that when the tubes are inflated the outer casing enclosing the tube assembly will be stretched taut thereabout, so as to form substantially planar sections between adjacent auxiliary tubes, each of said planar sections contacting said main tube tangentially along a longitudinal line.

5. Means for forming a void having a center section of square cross section and conical end sections, said means comprising an inflatable main rubber tube having a cylindrical center section and conical end sections, a plurality of auxiliary inflatable rubber tubes secured to said center section of said main tube, and an outer non-elastic, flexible casing enclosing all of said tubes, said auxiliary tubes being so spaced about said main tube as to distend said casing to provide a square cross section through the center portion of said casing when all of said tubes are inflated, the planar sides of said distended casing between adjacent auxiliary tubes being in tangential contact with said main tube.

6. Means for forming a void having a rectangular center section and a pair of tapered end sections in a precast concrete structural member of elongated rectangular shape with the smaller ends of said tapered end sections coincident with the ends of said concrete structural memher, said means comprising an inflatable main rubber tube having a cylindrical center section and a pair of tapered end sections, one of said tapered end sections having an open outer end, four elongated auxiliary inflatable rubber tubes or" less length than said cylindrical center section and of smaller transverse diameter than said main tube extending longitudinally of said cylindrical center section and spaced equally around the circumference thereof, the end of each of said auxiliary tubes closest to the open end of said one tapered end section being open, and an outer non-elastic, flexible casing enclosing said rubber tubes and being of a size and form to be stretched about said tube assembly including both of said tapered end sections when said tubes are inflated, said outer casing having one end open to permit access of air pressure means to the open end of each of said rubber tubes.

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